Embodiments of the present disclosure relate generally to magnetic resonance (MR) imaging, and more particularly to systems and methods for tracking an interventional device using MR imaging.
Medical interventional procedures are widely used for managing a plurality of life-threatening medical conditions. Particularly, minimally invasive interventional procedures are being exceedingly employed as cost-effective alternatives to invasive surgery. During an interventional procedure, an interventional device such as an endovascular catheter or needle may be inserted into a vascular structure that provides access to a region of interest (ROI), such as a cardiac region of a patient. The insertion as well as navigation of the interventional device within different branches of a vascular system, however, is a challenging procedure.
Accordingly, certain interventional techniques employ imaging modalities such as computed tomography (CT) and MR imaging (MRI) for generating high-fidelity images in near real-time to aid in guided interventions. Particularly, use of MRI during interventional procedures provides enhanced characterization of soft tissues, bone marrow, brain and spine without use of ionizing radiation typically used by CT systems. Additionally, MRI allows for accurate localization of the interventional device, which in turn, aids in accurate navigation of the interventional device within the vascular system without injuring surrounding tissues.
Conventionally, MRI systems employ passive and/or active techniques for tracking the interventional device within the patient's body. The passive techniques, for example, include use of paramagnetic markers and intravascular contrast agents for use in visualizing the interventional device. However, spatial and temporal resolutions achieved using the passive techniques are often acquisition dependent, and thus, may prove inadequate for distinguishing between the patient anatomy and the interventional device. Additionally, certain MRI systems employ active tracking techniques that typically provide higher signal-to-noise ratio and spatial and temporal resolutions than passive techniques. These active techniques, for example, include placing a radiofrequency (RF) receive coil on the interventional device and/or using a guide wire as a linear receive coil.
Generally, a small RF tracking coil is mounted on the interventional device such that the tracking coil is sensitive to protons in the immediate vicinity, for example, in surrounding blood or tissues. The MRI system, thus, tracks the position of the interventional device based on the position of the tracking coil. Specifically, the MRI system tracks the tracking coil by exciting spins of the protons and sequentially applying gradients in a plurality of orthogonal directions to localize the origin of the MR signals received from the tracking coil. To that end, the MRI system employs a separate tracking sequence with a fixed repetition period and at least three separate acquisitions to account for positional measurements along x, y and z directions.
Certain MRI systems implement the tracking sequence between successive image acquisitions. However, as typical image acquisition time extends over 1000 milliseconds, tracking of the interventional device may be delayed, thus making MR tracking unsuitable for real-time guidance of the interventional device. Certain other MRI systems interleave image acquisition with tracking to control latency. Interleaving of imaging and tracking acquisitions, however, interrupts imaging steady state. Accordingly, interleaving entails use of several dummy RF excitations to restore the imaging steady state for artifact-free imaging. The dummy RF excitations, however, add to the imaging time and tracking complexity.
Furthermore, conventional MRI systems typically employ a common Larmor or resonant frequency for imaging the surrounding tissue and tracking the interventional device, which may impede distinction between the interventional device and the surrounding tissue. Accordingly, a currently available approach is drawn to use of a single tracking coil adapted for use with both protons and other tracking nuclei. Merely using another tracking nuclei, however, may decrease MR coil quality factor leading to reduced coil sensitivity, which in turn, may hamper image quality.